Fig. 2

Association between CD21^−/low double-negative memory B cells and joint space narrowing score. A OPLS analysis depicting the association between the frequency of CD21^−/low double-negative memory cells (DN, CD27⁻IgD⁻) and clinical factors in eRA patients. B SF from swollen knees of rheumatoid arthritis patients (n = 5) was collected. Sample handling, staining and gating strategy as described in methods section. CD21^−/low B cells are increased in SF of estRA patients (C) and are mainly DN (D). The majority of the CD21^−/low DN are CD11c⁺Tbet⁺ (E) and the majority of the CD21⁻CD11c⁺Tbet⁺ are DN (F). G A representative FACS plot showing that RANKL⁺CD21^−/low B cells co-express CD11c. H The majority of CD21^−/low CD11c⁺RANKL⁺ cells are DN. B cell populations between two groups were compared using paired T test and Friedman test with Dunn’s multiple comparisons. *p < 0.05, ** p < 0.01. Between 2 × 10⁵ and 5.4 × 10⁵ events were recorded per sample. estRA, established rheumatoid arthritis; SF, synovial fluid; eRA, early rheumatoid arthritis